Abstract: The objects of this invention are new Saccharomyces cerevisiae yeast strains into which .alpha.-galactosidase gene (MEL.sup.+) has been transferred by using recombinant DNA methods. Baker's and distiller's yeasts producing .alpha.-galactosidase, are utilizable in the corresponding industry, because they are able to utilize the raffinose present in molasses, which results in greater yield of yeast (or ethanol) and reduction or elimination of the costs associated with biological oxygen demand (B.O.D.) in the effluent from factories. The improved ability of brewer's yeasts to produce .alpha.-galactosidase provides a sensitive method for monitoring pasteurization of beer.The new yeast strains prepared by using recombinant DNA methods produce more .alpha.-galactosidase than naturally occurring .alpha.-galactosidase producing yeast strains.Also methods for marking yeast strains and for producing stable transformants of yeasts are presented.

Abstract: A yeast expression and secretion vector is described. The vector carries a nucleotide sequence coding for a precursor polypeptide which includes the signal sequence of amylo-alpha-1-,-4-glucosidase from Saccharomyces diastaticus.

Abstract: In the initial stages of a fermentation of carbohydrate to form alcohol, the growth of the yeast is controlled by monitoring the pH value of a fermenting liquid or wort and controlling the supply of oxygen to the fermenting liquid or wort in accordance with the pH value. Preferably the temperature of the fermenting liquid is also controlled in dependence upon the pH value of the fermenting liquid or wort.